1. Field of the Invention and Related Art Statement
The present invention relates to a photoelectric measuring apparatus for use in an automatic chemical analyzer in which a plurality of substances contained in samples, i.e., a plurality of test items, are measured by using a plurality of measuring light beams having different wavelengths.
In Japanese Patent Publication No. 52,982/82, there is disclosed a photoelectric measuring apparatus for use in the chemical analyzer, in which a light beam transmitted through a test liquid is made incident upon a grating and is divided into a plurality of light beams having different wavelengths and these light beams are received by a plurality of photoelectric converting elements, i.e., light receiving elements. In this known photoelectric measuring apparatus, the wavelengths of the light beams emanating from the grating have been previously set and could not be changed simply. Therefore, the photoelectric measuring apparatus could not be easily adopted to the change or increase of the test items to be analyzed as well as to the change or improvement of measuring methods, so that it is necessary to select from the light beams having the previously determined wavelengths a light beam having a wavelength which is closest to a required wavelength. This results in a decrease in the sensitivity and accuracy of measurement. This will be further explained in detail hereinbelow by way of an example.
For instance, it is assumed that the measuring apparatus is designed to produce ten light beams having different wavelengths of 340, 380, 410, 480, 520, 540, 570, 600, 660 and 800 nm. When it is required to change the method of measuring serum iron from the TPTZ method having the maximum absorption at 600 nm as illustrated in FIG. 1 to the nitroso PSAP method having the maximum absorption at 750 nm shown in FIG. 2. In this case, since the photoelectric measuring apparatus does not generate the light beam having the wavelength of 750 nm, the PSAP method has to be carried out by using the light beam having the wavelength of 800 nm. Then, it is apparent that the measuring sensitivity is decreased by about 25% upon being compared with the case in which the standard wavelength of 750 nm is used. Therefore, the accuracy of the measurement is also decreased to a great extent.
In order to avoid the above mentioned drawback it may be considered that a larger number of light beams than those which are initially required are generated by the grating. However, this solution has another drawback that the number of light receiving elements becomes large and the photoelectric measuring apparatus is liable to be complicated in construction, large in size and expensive in cost.